Management of alloimmunized patients has been facilitated by further expansion of the HLA matched donor pool and continued growth of the autologous frozen platelet transfusion program. Studies of patients with non-lymphocytic leukemia have demostrated that the development of alloimmunization is not related to the number of platelet transfusions received. With few exceptions, patients who did not develop lymphocytotoxic antibody within 6-8 weeks of platelet transfusion never developed antibody despite subsequent transfusions, possibly suggesting a state of immune tolerance to histocompatibility antigens. A randomized study comparing the rate of alloimmunization in patients receiving lymphocyte depleted and "standard" platelet concentrations is in progress. Platelet cryopreservation using glycerol-glucose as the cryoprotective agents has demonstrated good freeze-thaw recovery but significant loss of ATP and morphologic integrity. Indium labeled granulocytes migrate to infected sites within 30 minutes of transfusion and have been shown to be a relatively simple and reliable label permitting excellent scanning and kinetic analysis. Studies are in progress using this technique to determine the effect of alloimmunization on granulocyte migration after transfusion.